(198) Glucose metabolism across the murine implantation site

S. Chen¹ and M. Dean^1,2

¹Department of Animal Sciences, College of Agricultural, Consumer and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA

² Division of Nutritional Science, College of Agricultural, Consumer and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA


Abstract Text:

Pregnancy loss is one of the significant global issues that affects women’s health and population growth. Pregnancy loss is more common than many people realize. Approximately 30% of pregnancies fail after human chorionic gonadotrophin (hCG) is detectable in urine. How many are lost before hCG detection is unknown, but it is estimated that 50% of all pregnancies in women fail. Most of these losses occur during implantation. Glucose is important for both the embryo and the maternal uterus in early pregnancy. Embryonic glucose uptake starts to increase dramatically as the embryo transitions into a blastocyst and begins to implant. Decidualization also dramatically changes glucose metabolism in the uterine stroma due to an increased glucose influx through glycolysis and the pentose phosphate pathway. The uterus lacks the enzymes to make glucose, which means all glucose used by the uterus or by the embryo must come from the maternal circulation. We have shown that the uterus stores glycogen. The uterine stroma stored sevenfold glycogen after decidualization. It is unclear why the decidua, while catalyzing glucose through multiple pathways, would also store glucose. This led us to hypothesize that glycogen serves to regulate glucose metabolism in a spatial and temporal manner and provides the right amount of glucose at the right time during implantation. Therefore, the objective of this study was to localize glycogen and key glucose-metabolizing enzymes across the murine implantation site.

Female mice were housed with males and the day a vaginal plug found was considered as 0.5 days post coitum (DPC). The implantation sites were collected at 7.5 DPC. Implantation sites were fixed, embedded, sectioned across the implantation site, and histologically analyzed. Glycogen was detected and localized by diastase-labile periodic acid–Schiff (PAS) staining, and glycogen-metabolizing enzymes and glucose-metabolizing enzymes were localized by immunostaining. Our results showed that the undecidualized stroma adjacent to the myometrium did not stain for glycogen or relevant enzymes, suggesting low levels of glucose metabolism. Diastase-labile PAS staining indicated high glycogen levels in the outer decidual and lower levels in the inner decidua near the embryo. There was diastase-resistant PAS staining immediately around the embryo, suggesting the presence of other glycomolecules. Further, immunostaining results indicated that glycogen synthase (GYS, rate-limiting enzyme in glycogen synthesis) and glycogen phosphorylase (PYGM, rate-limiting enzyme in glycogen breakdown) were present mostly in the outer portion of the decidua and lower in the inner decidual cells closer to the embryo, which agrees with the diastase-labile PAS staining. Pyruvate kinase (PKM2, rate-limiting enzyme in glycolysis) showed the opposite pattern, being highly expressed in the inner decidual cells near the embryo and decreased expression away from the embryo. Overall, our results suggested that glycogen and glucose metabolism are spatially regulated in the decidua.  On 7.5 DPC, the outer decidua stores glycogen, likely to support embryonic growth later. While the inner decidua is catabolizing glucose via glycolysis, possibly to support embryonic growth. Future studies will focus on the glycogen-related and glucose-related RNA and metabolite levels across the implantation site with spatial transcriptomics and mass spectrometric (MS) techniques.

Keywords: Glycogen, Glucose, Decidualization, Implantation Site

Financial Support: FIRE award from the College of ACES at the University of Illinois